1. Field of the Invention
The present invention relates to an apparatus and method of writing a pattern by light irradiation to a photosensitive material.
2. Description of the Background Art
Conventionally well known are techniques for applying a light beam modulated by a spatial light modulator such as a digital micromirror device (DMD) onto a photoresist film formed on a substrate such as a semiconductor substrate or a printed circuit board.
Japanese Patent Application Laid-open No. 62-21220 discloses a technique for writing a fine pattern by applying a light beam which is spatially modulated by a micromirror group of a DMD onto a photosensitive material and by moving the photosensitive material and controlling a signal given to the DMD every time the photosensitive material passes a predetermined distance.
Also, Japanese Patent Application Laid-open No. 2001-133893 suggests a technique for writing a finer pattern by tilting an image formed by a DMD on a photosensitive material at 45 degrees relative to a main scanning direction. FIG. 1 is a diagram for explaining the pattern writing suggested in Japanese Patent Application Laid-open No. 2001-133893. In an image 90 formed by a DMD on a photosensitive material in FIG. 1, an irradiation region group 91 arranged in a row in a direction perpendicular to the main scanning direction corresponds to a set of main scan mirrors of the DMD, and another irradiation region group 92 which is arranged in the direction perpendicular to the main scanning direction and each of whose regions is located between adjacent regions of the irradiation region group 91, corresponds to a set of interpolation main scan mirrors of the DMD. The image 90 is scanned on the photosensitive material in a direction indicated by arrow 94, i.e., the main scanning direction, and at some point in time, a space between adjacent regions on the photosensitive material which are exposed by the respective main scan mirrors is exposed by each of the interpolation main scan mirrors. This achieves fine pattern writing.
When changing an image (i.e., a pattern indicating spatial modulation of a light beam) formed on a photosensitive material, the spatial light modulator such as a DMD requires, for example, time to write data into memory cells each corresponding to one light modulating element and time between receiving a reset pulse and holding each light modulating element in position (i.e., fixing the position (orientation) of each micromirror of the DMD). However, there are technical limitations to what we can do to shorten such times. Thus, it is not easy to drive the spatial light modulator at higher speed and thereby to speed up pattern writing by exposure.
For example, in a DMD where 16 blocks of micromirrors, each block containing 48 rows and 1024 columns of micromirrors, are arranged in a column direction to form a matrix of 768 rows and 1024 columns, control is exercised block by block. However, addressing and writing data into the blocks is generally performed on line by line; therefore, when this DMD is employed in the technique shown in FIG. 1, data must be written into every block containing part of the main scan mirrors and the interpolation main scan mirrors, which makes it difficult to achieve high speed pattern writing.